A TAP orbit has been proposed that can provide substantially continuous imaging and/or communications coverage for a polar region using a two satellite constellation, both of the two satellites being in the same orbital plane, the orbit having a period of about 16 hours. Trishschenko, et al., “Three-Apogee 16-h Highly Elliptical Orbit as Optimal Choice for Continuous Meteorological Imaging of Polar Regions,” Journal of Atmospheric and Oceanic Technology, Vol. 28, November 2011, hereinbelow, “Trishschenko”. A characteristic of the proposed constellation is that one or the other of the two satellites is near orbit apogee at eight hour intervals, that is, three times per day. Since one or the other of the spacecraft is near apogee at all times, continuous coverage of the region of Earth's surface beneath the apogee is provided. By appropriate selection of the orbital plane's argument of perigee, the orbit apogee may be positioned over the Arctic or Antarctic polar regions. For example where Arctic coverage is desired, the argument of perigee is preferably set to about 270°. Where Antarctic coverage is desired, the argument of perigee is preferably set to about 90°.
The TAP orbit has an inclination greater than 60°, typically in the range of 63.4° to 70°, an eccentricity of about 0.55, a perigee altitude in the range of approximately 7000 to 15000 km (typically about 8100 km), and an apogee altitude in the range of 35,000 km to 50,000 km (typically about 43,500 km). Trishschenko, page 1412, Table 1. When a pair of satellites is disposed and maintained in such an orbit, spaced apart by eight hours (one half of the orbit period) and the argument of perigee is approximately 270°, substantially uninterrupted coverage of the Arctic region at or above 60° N latitude may be provided. Similarly, when the argument of perigee is approximately 90°, substantially uninterrupted coverage of the Antarctic region at or below 60° S latitude may be provided.
In the absence of orbit maintenance, a satellite initially disposed in a TAP orbit described above will experience considerable natural drift from desired parameters of amount of orbit inclination, argument of perigee, perigee and apogee altitude as a result of gravitational influence of the Earth, moon and sun. In the absence of the presently disclosed techniques, the annual orbit maintenance delta V requirements required to compensate for this drift are estimated as follows:
Delta-VControlled Parameter(m/s/yr)Inclination5Argument of Perigee54Perigee Altitude23Apogee Altitude7Total89
The above listed delta V requirements imply a very significant propellant mass, for a 10-15 year mission life, which the present techniques aimed to reduce.